HEAT, TEMPERATURE, PHASE CHANGE HEAT A form of energy that a substance has because of the motion of its molecules. - When a substance gains heat its molecules move more vigorously. - When a substance loses heat its molecular action decreases. - Absolute Zero is the point at which all molecular motion would stop. (no heat left!!) TEMPERATURE Definition: average kinetic energy of the particles that make up a substance Temp is a measure of how hot or cold something is. It is measured in degrees The size of degrees may vary depending on the temperature scale (Fahrenheit, Celsius, or Kelvin) How is temp measured?? Fahrenheit Celsius Kelvin Which one is not metric? Fahrenheit Scale Major references points Freezing point of water: Boiling point of water: There 32ºF 212ºF are 180ºF between freezing and boiling points. Celsius Scale A fixed point of where water freezes is the zero point Freezing point of water: Boiling point of water: There 0ºC 100ºC are 100ºC between freezing and boiling points, making this scale closely linked to the decimal system. Kelvin The temperature at which molecular motion stops is the zero point Absolute Zero (no heat) 0K Freezing point of water: Boiling point of water: There 273 K 373 K are 100 K between freezing and boiling points making this scale closely linked to the metric system. Comparison of Temperature Scales -460º Heat vs. Temperature Temperature does not always change when heat is added or taken away There is no change in temperature during a phase change - all heat energy is used to break bonds between molecules, not to raise the temperature. Are heat and temp the same? Heat and temp are related, but they are NOT the same! Heat is dependent upon what kind of material you are measuring and how much of the material you have. Example: Imagine that you fill a tea cup and a bath tub with the exact same water that has been heated to the exact same temperature. Will they cool down at the same rate? What happens when heat is applied to matter? Particle Theory of Matter Everything is made of matter which are tiny particles that are… in constant motion held together by strong force have spaces between them States of Matter SOLID Shape and volume is definite Particle distance is packed in fixed positions Particles vibrate in place States of Matter LIQUID Takes the shape of the container Definite volume Particle distance is close Particles slide over one another freely States of Matter GAS Takes the shape and volume of the container Particle distance is spread out or squeezed into a container Particles are able to fly at high speeds in all directions Heat added to the states of matter… Changes in Matter • A substance changes state when its thermal energy increases or decreases by a sufficient amount (absorbing or releasing HEAT) Phase changes are: melting/freezing, vaporizing/condensing, and sublimation Melting solid to a liquid *** Interesting Fact: different substances have different melting points, it depends on how strongly the particles of the substances are attracted to one another Silver melts at 962ºC Water melts at 0ºC Freezing a liquid to a solid *** Interesting Fact: freezing is the opposite of melting; therefore, a substances “freezing point” is the same as its melting point Freezing Rain Vaporization a liquid to a gas Evaporation: surface only Boiling: throughout Condensation a gas to a liquid Interesting Fact: condensation is the opposite of vaporization Examples of condensation are steam, clouds, and mist; you cannot see water vapor it is a gas Sublimation a solid directly to a gas; there is not liquid phase Interesting Fact: an example of sublimation is dry ice Dry ice is solid carbon dioxide that changes directly to carbon dioxide gas when it is in room temperature Label each letter on your graph with a phase or a phase change. What happens to the temperature during a phase change?